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Security Classification

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Keywords

Background

Concerns regarding the competitiveness of the defense of the NATO nations resources are steadily on the rise as non-allied countries continue to strengthen their capabilities towards hypersonic penetrating weapons, being able to shorten the time between launch and strike, reducing the effectiveness of counter measures. The design of defense systems that operate at high speeds is challenging. In particular, heating rates due to fully turbulent hypersonic boundary layers and thermo-chemical effects significantly challenge structural integrity of high- speed vehicles and reduce the available payload size. Currently, large discrepancies exist between predicted and measured turbulent aerodynamic heating and drag over high speed projectiles and vehicles, warranting the urgent development and improvement of multi-fidelity computational models to enable hypersonic vehicle design. More complications arise in particular phenomena such as molecular dissociation and recombination, which have received very little attention in the fully turbulent high speed regime. Ultimately, a fundamental understanding of this peculiar flow condition can only occur with a synergistic effort among world-renowned scientists in the field. This will enable to improve our prediction capabilities and hence allow a more effective vehicle design from an aerodynamic and materials perspective.

Objectives

The contemplated Exploration Team extends preceding AVT research activities on predicting hypersonic boundary layer transition to a flow regime unavoidable for high Reynolds number flows - the fully turbulent boundary layer. It also focuses on the fundamental understanding of the small-scale structure of compressible turbulence.
The near-term goals of the ET for 2019 are to:
(a) Determine the state of the art in: wall-bounded and homogenous-isotropic high-Mach-number turbulence modeling, turbulence-chemistry interactions in real-gas flows, experimental flow diagnostics for extraction of first and second-order turbulent statistics in hypersonic environments;
(b) Identify various teams within the ET focusing on the aforementioned sub-topics;
(c) Develop a tentative 3-year plan coordinating experimental, computational and modeling efforts across NATO nations with the goal of increasing the diversity of the approaches and the enrollment of more NATO nations and partners. Such efforts are expected to result in periodic publications in special issues of peer-reviewed journals.
A report detailing the outcome of such near-term tasks, outlining a tentative plan for this task will be provided by May 15th to the NATO panel and presented in the AVT Panel Meeting in May 20th in Slovakia.
The long-term scientific outcome of the ET, as it transitions to RTG, is to develop the next generation of turbulence modelling techniques applicable to different flow conditions that can encompass high speed flight and thus improve engineering design tools for vehicles operating at hypersonic conditions. The activity will enhance partnerships among researchers of allied nations, experts in both experimental and numerical fields. A final report detailing the progress of the team will conclude the activity.

Topics

The Exploration Team would focus on turbulence modelling at high speeds. One of the objectives is to enhance the fundamental knowledge of near-wall hypersonic turbulence to inform both Large-Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) modelling of hydrodynamic and thermal Reynolds stresses at different pressure gradient (Favorable, Adverse and Zero) regimes expected to be relevant to hypersonic flight. As the research progresses, the proposed AVT Task would analyze the effects of complex geometries in high speed turbulence.
Another goal of the proposed Task is high altitude flight focusing on real-gas effects and chemical reactions in fully turbulent conditions, enabling the prediction of oxidation rates of thermal protection shields, such as carbon/carbon ceramics, and their survivability. As such, it is at the cross-roads between aerodynamics and materials sciences.
For the success of the proposed task, these two efforts should be assisted by experimental diagnostics for turbulence to be performed at the existent ground facilities located at different NATO nations.